Radiation sensor to detect different targeted radiation and radiation detection system including the radiation sensor

ABSTRACT

A radiation sensor can include a first layer and a second layer. The first layer can include a first scintillation material to produce first light in response to receiving a first targeted radiation, and the second layer can include a second scintillation material to produce second light in response to receiving a second targeted radiation. The first scintillation material can be different from the second scintillation material, and the first targeted radiation can be different from the second targeted radiation. The first layer can be configured to receive and transmit the second light. In an embodiment, the radiation sensor can be part of a radiation detection system that includes a photosensor that can produce an electronic pulse in response to the first and second lights. A method of detecting radiation can include using the radiation detection system to distinguish different radiations by differences in pulse shape.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119(e) to U.S. PatentApplication No. 61/350,219 entitled “Radiation Sensor to DetectDifferent Targeted Radiation and Radiation Detection System IncludingThe Radiation Sensor,” by Kusner, filed Jun. 1, 2010, which is assignedto the current assignee hereof and incorporated herein by reference inits entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to radiation sensors, and moreparticularly, radiation sensors configured to detect different targetedradiation, and radiation detection systems including such radiationsensors.

BACKGROUND

Radiation detection systems are used in a variety of applications. Forexample, scintillators can be used for medical imaging and for welllogging in the oil and gas industry. A scintillation member can beeffective for detecting gamma rays or neutron radiation. Generally, thescintillation member is enclosed in a casing or sleeve that includes awindow to permit radiation-induced scintillation light to pass out ofthe package. The light is detected by a photosensor, such as aphotomultiplier tube. The photomultiplier tube can convert the photonsemitted from the scintillation member into electrical pulses. Theelectrical pulses are can be processed by associated electronics and maybe registered as counts that are transmitted to analyzing equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be better understood, and its numerousfeatures and advantages made apparent to those skilled in the art byreferencing the accompanying drawings.

FIG. 1 includes a schematic diagram illustrating a radiation detectionsystem.

FIG. 2 includes a schematic diagram illustrating another radiationdetection system.

FIG. 3 includes an illustration of a cross-sectional view of anapparatus that includes a radiation sensor and a photosensor that can beused with the radiation detection system of FIG. 1.

FIG. 4 includes an illustration of a cross-sectional view of anapparatus that includes a radiation sensor and photosensors that can beused with the radiation detection system of FIG. 2.

FIG. 5 includes an illustration of a perspective view of an assemblythat can be used as a radiation sensor within a radiation detectionsystem in accordance with a particular embodiment.

FIG. 6 includes spectra obtained using the assembly of FIG. 5.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

The following description in combination with the figures is provided toassist in understanding the teachings disclosed herein. The followingdiscussion will focus on specific implementations and embodiments of theteachings. This focus is provided to assist in describing the teachingsand should not be interpreted as a limitation on the scope orapplicability of the teachings.

As used herein, the terms “comprises,” “comprising,” “includes,”“including,” “has,” “having,” or any other variation thereof, areintended to cover a non-exclusive inclusion. For example, a process,method, article, or apparatus that comprises a list of features is notnecessarily limited only to those features but may include otherfeatures not expressly listed or inherent to such process, method,article, or apparatus. Further, unless expressly stated to the contrary,“or” refers to an inclusive-or and not to an exclusive-or. For example,a condition A or B is satisfied by any one of the following: A is true(or present) and B is false (or not present), A is false (or notpresent) and B is true (or present), and both A and B are true (orpresent).

The use of “a” or “an” is employed to describe elements and componentsdescribed herein. This is done merely for convenience and to give ageneral sense of the scope of the invention. This description should beread to include one or at least one and the singular also includes theplural, or vice versa, unless it is clear that it is meant otherwise.For example, when a single item is described herein, more than one ofthe item may be used in place of a single item. Similarly, where morethan one of the item is described herein, a single item may besubstituted.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. The materials, methods, andexamples are illustrative only and not intended to be limiting. To theextent not described herein, many details regarding specific materialsand processing acts are conventional and may be found in reference booksand other sources within the scintillating and radiation detection arts.

FIG. 1 illustrates a particular embodiment of a radiation detectionsystem 100. The radiation detection system 100 can include a radiationsensor 101 coupled to a photosensor 105. In an embodiment, the radiationdetection system 100 includes a light pipe 103. Though the radiationsensor 101, the light pipe 103, and the photosensor 105 are illustratedseparate from each other, the radiation sensor 101 and the photosensor105 can be coupled to each other directly or via the light pipe 103. Inan embodiment, the radiation sensor 101 and the photosensor 105 can becoupled to the light pipe 103 using an optical gel, bonding agent,fitted structural components, or any combination thereof.

The radiation sensor 101 can include a scintillation member 107 housedwithin a casing 113. The scintillation member 107 can detect neutronradiation (for example, thermal neutrons and fast neutrons), gammaradiation, other targeted radiation, or any combination thereof. In anembodiment, the scintillation member 107 can include a plurality ofdifferent scintillation materials. Details regarding the composition ofthe scintillation member 107 are described in more detail later in thisspecification. In an embodiment, the scintillation member 107 has alength, L, and a width, W, as illustrated in FIG. 1. In a particularembodiment, the scintillation member 107 has a length of at leastapproximately 0.5 meters. For example, the scintillation member 107 hasa length of at least approximately 0.7 meters or at least approximately1.1 meters. In another example, the scintillation material extendsgreater than 2 meters, such as greater than 3 meters, or another lengthcorresponding to a height of a person, a vehicle, such as an automobile,a truck, a watercraft, a rail car, an aircraft, other suitable cargovehicle, or any combination thereof. In another embodiment, thescintillation member 107 can have a width, W, substantiallyperpendicular to the length, L, where the width is at leastapproximately 0.01 meters and at most equal to the length L. Forexample, the scintillation member 107 can be a polygon having a width ofat least approximately 0.01 meters. In another example, thescintillation member 107 can be substantially cylindrical and can have adiameter, a particular type of width, of at least approximately 0.1meters.

In a particular embodiment, the radiation sensor 101 can be surroundedby a neutron moderator (not illustrated in FIG. 1), such as polyethyleneor another material, to convert fast neutrons into thermal neutrons,when the particular targeted radiation to be detected includes fastneutrons. The radiation sensor 101 can also include a reflector 109. Inone embodiment, the casing 113 can include a material that issubstantially non-reactive with the scintillation member 107,environmental conditions, or any combination thereof. For example, thecasing material can include stainless steel, plastic, another suitablematerial, or any combination thereof. A shock-absorbing member 111 maybe disposed between the casing 113 and the reflector 109. Further, thecasing 113 can include an output window 115 that is interfaced to an endof the scintillation member 107. The output window 115 can include glassor another transparent or translucent material suitable to allow photonsemitted by the radiation sensor 101 to pass toward the photosensor 105.An optical interface, such as silicone rubber, can be disposed betweenthe scintillation member 107 and the output window 115. The opticalinterface can be polarized to align the reflective indices of thescintillation member 107 and the output window 115.

As illustrated, the light pipe 103 is disposed between the photosensor105 and the radiation sensor 101 and facilitates optical couplingbetween the photosensor 105 and the radiation sensor 101. In anembodiment, the light pipe 103 includes a quartz light pipe, plasticlight pipe, or another light pipe. In another embodiment, the light pipe103 can include a silicone rubber interface that optically couples anoutput window 115 of the radiation sensor 101 with the input window 108of the photosensor 105. In a further embodiment, a plurality of lightpipes is disposed between the photosensor 105 and the radiation sensor101.

The photosensor 105 can include a photodiode, a photomultiplier tube(“PMT”), a silicon photomultiplier (“SiPM”), an avalanche photodiode(“APD”), or a hybrid PMT that includes a photocathode and an electronsensor. The photosensor 105 can be housed within a tube or housing madeof a material capable of protecting electronics associated with thephotosensor 105, such as a metal, metal alloy, another material, or anycombination thereof.

The photosensor 105 can include an input window 108, such as a windowthat can include any of the materials described with respect to theoutput window 115. The input window 108 and the output window 115 canhave substantially the same composition or can have differentcompositions. In a particular, illustrative embodiment, the photosensor105 receives light from the radiation sensor 101 via the input window108. The output window 115 or the input window 108 may have a discretefilter material incorporated therein. In another embodiment, a filtermay be another location between the scintillation member 107 and aphotocathode 118 of the photosensor 105. In a particular embodiment, thefilter material or discrete filter can be used to allow some light, butnot all light to pass. For example, a blue filter material or bluefilter may allow blue light to pass, but block another spectrum light,for example, red light.

In a particular embodiment, the photosensor 105 can receive lightemitted by the radiation sensor 101 as a result of the scintillationmember 107 receiving gamma radiation, neutron radiation, otherparticular radiation, or any combination thereof. The emitted lightphotons can strike the photocathode 118 of the photosensor 105 andtransfer energy to electrons of the photocathode 118. Thus, someelectrons are emitted as free electrons from a surface of thephotocathode 118 that is opposite the input window 108. In a particularembodiment, the surface of the photocathode 118 can include a layer ofelectropositive material that can facilitate emission of the electronsfrom the surface of the photocathode 118.

Electrons emitted by the photocathode 118 are collected at an anode ofthe photosensor 105, and signals, in the form of one or more electronicpulses, are sent to the processing module 120 via the output 110. In anexample, a voltage 121, such as a supply voltage or another voltage, isapplied to the photocathode 118. Electrons emitted from the surface ofthe photocathode 118 can be accelerated, by the voltage 121 and strikethe surface of an electron sensor 119. In addition, a voltage 122, suchas a reverse bias voltage or another voltage, can be applied to theelectron sensor 119. Energy from electrons entering the electron sensorcan produce charge carriers that are removed from the electron sensor119 by the reverse bias voltage 122, thus creating an electrical pulse.The processing module 120 can include a pulse analyzer that can analyzethe electronic pulse from the photosensor 105 and identify the type ofradiation to which the electronic pulse corresponds.

The photosensor 105 can be coupled to a processing module 120 thatincludes a pulse analyzer in a particular embodiment. As illustrated inthe embodiment of FIG. 1, an electronic pulse or another signal is sentfrom the photosensor 105 to the pulse analyzer, via an output 110, whichcan be in the form of a coaxial cable or other electronic transmissionmedium to transmit electrical signals from the photosensor 105 to thepulse analyzer. The pulse analyzer can be configured to analyze pulsesreceived from the photosensor 105 to determine the type of radiation towhich the pulse corresponds. The pulse analyzer can be coupled toradiation counters 182 and 184, via the processing module 120, whichsends a signal to the radiation counter 182 when one type of radiationis detected, and sends a signal to the radiation counter 184 whenanother type of radiation is detected. In a particular embodiment, theradiation counter 182 is a neutron counter, and the radiation counter184 is a gamma radiation counter. In another embodiment, one or both ofthe radiation counters may be replaced by another counter for adifferent targeted radiation (for example, x-ray, beta particles, etc.).

The processing module 120 can include hardware, firmware, or anycombination thereof that is configured to perform operations asdescribed later in this specification. Examples of such hardware andfirmware include circuits within one or more integrated circuits,one-time programmable devices, field programmable gate arrays,application-specific integrated circuits, and the like. After readingthis specification, skilled artisans will appreciate that othercomponents can be used. In another embodiment, the processing module 120can include a central processing unit, a graphics processing unit,another suitable processing unit, or any combination thereof. In stillanother embodiment, the processing module 120 can be coupled to astorage device 130, which can be a tangible processor-readable medium.The storage device 130 can include a hard disk, a read-only memory,random-access memory, a memory drive within a storage network, or thelike. The storage device 130 can include code. The processing module 120can retrieve code from the storage device 130, wherein the code includesinstructions to carry out the operations. The processing module 120, thestorage device 130, or both may be coupled to other equipment within theradiation detection system 100 or may be coupled to networking equipment(not illustrated).

FIG. 2 illustrates another embodiment of a radiation detection system200 that similar to the radiation detection system 100 except that theradiation detection system 200 includes two photosensors 205 and 255coupled to a radiation sensor 201. Many of the functions, compositions,and configurations of components within the radiation detection system200 will be described with respect to corresponding components of theradiation detection system 100.

With respect to the radiation sensor 201, its configuration may or maynot be modified to allow it to be coupled to the photosensors 205 and255. The scintillation member 207 can perform any of the functions ofthe scintillation member 107. The radiation sensor 201 can be surroundedby a neutron moderator (not illustrated in FIG. 2) that performs any ofthe functions or include any of the materials described with respect tothe neutron moderator described with respect to the radiation sensor101. A reflector 209, a shock-absorbing member 211, and the casing 213can perform any of the functions of and include any of the materialspreviously described with respect to the reflector 109, theshock-absorbing member 111, and the casing 113, respectively. Theconfiguration of the reflector 209, a shock-absorbing member 211, andthe casing 213 may be modified to allow the photosensors 205 and 255 tobe coupled to the radiation sensor 201. Output windows 215 and 265 canperform any of the functions of and include any of the materials usedwithin the output window 115. Light pipes 203 and 253 can perform any ofthe functions of and include any of the materials used within the lightpipe 103. The output window 215 may have the same or differentconfiguration or materials as compared to the output window 265, and thelight pipe 203 may have the same or different configuration or materialsas compared to the light pipe 253.

The photosensors 205 and 255 can perform any of the functions andinclude any of the components as described with respect to thephotosensor 105. The photosensors 205 and 255 can be of the same type ordifferent types as compared to each other. Selection of photosensors 205and 255 is addressed later in this specification. Input windows 208 and258 can perform any of the functions of and include any of the materialsused with the input window 108. The output window 215 or 265, the inputwindow 208 or 258, or any combination of such window may have a filtermaterial incorporated therein. In another embodiment, one or morediscrete filters may be at a location between the scintillation member207 and the photocathode 218 of the photosensor 205 and between thescintillation member 207 and the photocathode 268 of the photosensor255. In a particular embodiment, the radiation detection system 200 caninclude different filtering materials or discrete filters, such that thephotosensor 205 receives blue light and substantially no or asignificantly reduced amount of green light, and the photosensor 255receives green light and substantially no or a significantly reducedamount of blue light. Clearly, other filter combinations may be used ifneeded or desired. Photocathodes 218 and 268 can perform any of thefunctions of and include any of the materials used within thephotocathode 118. Electron sensors 219 and 269 can perform any of thefunctions of and include any of the materials used within the electronsensor 119.

An output 210 is coupled to the electron sensor 219 and a processingmodule 220, and an output 260 is coupled to the electron sensor 269 andthe processing module 220. The outputs 210 and 260 can perform any ofthe functions and any include any of the materials used within theoutput 110. The processing module 220, a storage device 230, a radiationcounter 282, and a radiation counter 284 can perform any of thefunctions of and be configured as described with respect to theprocessing module 120, the storage device 130, the radiation counter182, and the radiation counter 184, respectively.

The scintillation members 107 and 207 can include a composite of atleast two different scintillation materials. In a particular embodiment,the scintillation members 107 and 207 can include a laminate ofalternating layers, wherein some layers are more sensitive to aparticular targeted radiation, and other layers are more sensitive to adifferent targeted radiation. In a particular embodiment, some layersare more sensitive to gamma radiation and less sensitive to neutronradiation, whereas other layers are more sensitive to neutron radiationand less sensitive to gamma radiation. FIGS. 3 and 4 illustrateparticular radiation sensors that can include a scintillating member 107or 207.

FIG. 3 includes an illustration of a cross-sectional view of anapparatus 300 that includes a radiation sensor 310 and photosensor 340that can be used with the radiation detection system 100 as illustratedin FIG. 1. The radiation sensor 310 can include a scintillation member320 than includes alternating neutron sensitive layers 322 and gammasensitive layers 324. A photosensor 340 can be coupled to the ends ofthe layers 322 and 324. A reflector 350 can be coupled to opposite endsof the layers 322 and 324 and along sides of the outermost gammasensitive layers 324 of the scintillation member 320. In the illustratedembodiment, a neutron moderator 360 surrounds the scintillation member320.

The neutron sensitive layers 322 can be configured to producescintillating light in response to receiving neutron radiation. Thescintillating light produced by the neutron sensitive layers 322 caninclude visible light or other radiation (such as ultravioletradiation). In a particular embodiment, the neutron sensitive layers 322can include a component, such as ⁶Li or ¹⁰B (in ionized or non-ionizedform), to produce a secondary particle in response to absorbing aneutron. The scintillation material can also include another component,such as ZnS, CaWO₄, Y₂SiO₅, ZnO, ZnCdS, or another substance to producelight in response to receiving the secondary particle.

The neutron sensitive layers 322 can include scintillation material thatincludes a dopant that allows for or enhances the scintillation processin the material and may further cause the spectrum of the emitted lightto have desirable properties such as matching the absorption spectrum ofother elements in the detector. The dopant can be as a transition metal,a rare earth metal, or another element. Unless otherwise noted herein,the term “rare earth” oxide generally denotes the lanthanide serieselements, as well as Y and Sc. In a particular embodiment, the neutronsensitive layers 322 can include ZnS(Ag), ZnS(Cu), ZnS(Ti); Y₂SiO₅(Ce),ZnO(Ga), ZnCdS(Cu), or CaF₂(Eu) where the element within the parenthesesis the dopant.

The neutron sensitive layer can be within a polymer matrix. The polymermatrix can include polyvinyl toluene (“PVT”), a polystyrene (“PS”), apolymethylmethacrylate (“PMMA”), or any combination thereof. The polymermatrix can be in the form of a cast sheet, fibers, or another suitableform. When the neutron sensitive layers 322 are in the form of fibers,the fibers can have cross sections that are substantially rectangular,substantially round, or another shape.

The gamma sensitive layers 324 can be configured to producescintillating light in response to receiving gamma radiation. Thescintillating light produced by the gamma sensitive layers 324 caninclude visible light or other radiation (such as ultravioletradiation). The scintillating light produced by the gamma sensitivelayers 324 can be the same or different from the scintillating lightproduced by the neutron sensitive layers 322. In a particularembodiment, the gamma sensitive layers 324 can include a scintillationmaterial different from the scintillation material within the neutronsensitive layers 322.

The gamma sensitive layers 324 can include an organic scintillationmaterial. In an embodiment, the organic scintillation material caninclude an aromatic compound. In a particular embodiment, the aromaticcompound can be a homoaromatic compound or a heteroaromatic compound. Ina more particular embodiment, the aromatic compound includes a phenyl orpyrazoline aromatic compound. In another particular embodiment, theorganic scintillation material can include1,4-bis(5-phenyloxazol-2-yl)benzene, 2,5-diphenyloxazole, p-terphenyl,naphthalene, 1,4-bis[2-methylstyryl benzene] (“bis-MSB”), and1,1,4,4-tetraphenyl-1,3 butadiene (“TPB”), another suitable organiccompound, or any combination thereof. The organic scintillation materialcan be mixed into a solvent, such as toluene, 1-phenyl-1-xylyl ethane(“PXE”), a linear alkyl benzene (“LAB”), or another solvent. In anembodiment, the combination of the organic scintillation material andthe solvent can be mixed into and dissolve within the polymer matrix.

The gamma sensitive layer 324 can include a polymer matrix can includePVT, PS, PMMA, another suitable polymer, or any copolymer thereof. Thepolymer matrix can be in the form of a cast sheet, fibers, or anothersuitable form. When the gamma sensitive layers 324 are in the form offibers, the fibers can have cross-sections that are substantiallyrectangular, substantially round, or another shape. In a particularembodiment, a wavelength-shifting fiber can be used in addition toanother fiber, such as a scintillation fiber, and include a plurality ofmaterials that includes two materials having different refractiveindices. For example, a wavelength shifting fiber can include a PS coreclad with an acrylic material, such as PMMA. In another particularembodiment, an additional cladding may be used, such as a fluoropolymer.In another particular embodiment, the gamma sensitive layers 324 caninclude a cast sheet, such as a doped polymer sheet that has anabsorption spectrum that substantially matches an emission spectrum of ascintillation material of the gamma sensitive layers 324.

The gamma sensitive layers 324 can include one or more fluorescentmaterials. In a particular embodiment, the gamma sensitive layers 324can include p-terphenyl or bis-MSB as a fluorescent material. Thefluorescent light may be green and have an emission maximum in a rangeof approximately 500 nm to approximately 600 nm. In a particularembodiment, the gamma sensitive layers 324 can include p-terphenyl,bis-MSB, and a benzoxanthene-dicarboxylic acid imide within a PVTmatrix. Benzoxanthene-dicarboxylic acid imides are described in U.S.Pat. No. 3,741,971, and the formula below is for a particularbenzoxanthene-dicarboxylic acid imide.

The gamma sensitive layer 324 may include an additional fluorescentmaterial if needed or desired. The additional fluorescent material canbe tailored to shift the wavelength of scintillation light generatedfrom neutron radiation to a different wavelength. In a particularembodiment, the fluorescent light may be green and have an emissionmaximum in a range of approximately 500 nm to approximately 600 nm. In aparticular embodiment, the gamma sensitive layers 324 can includep-terphenyl, bis-MSB, and a benzoxanthene-dicarboxylic acid imide as afluorescent material. Thus, in a particular embodiment, scintillatinglight from both gamma radiation and neutron radiation can be shifted togreen light within the gamma sensitive layers 324, and therefore, thelight from the fluorescent materials may have emission maxima withinapproximately 100 nm of each other. In a particular embodiment, thephotosensor 340 can have a quantum efficiency that is relatively higherfor green light than other light.

In another embodiment, the photosensor 340 may have a quantum efficiencythat is relatively higher for another color of light, such as bluelight. In this embodiment, the fluorescent materials can be selectedsuch that scintillating light is shifted to blue light (emission maximumat approximately 400 nm to approximately 500 nm). After reading thisspecification, skilled artisans will be able to select fluorescentmaterials to achieve a desired range of wavelengths of light to betransmitted along the gamma sensitive layers 324.

In another embodiment, the gamma sensitive layers 324 can include aninorganic scintillation material. In a particular embodiment, the gammasensitive layers 324 can include inorganic scintillation particleswithin a polymer matrix. The inorganic scintillation particles caninclude a sodium iodide, a calcium fluoride, a cesium iodide, a cesiumlithium elpasolite, a lanthanum bromide, a lanthanum chloride, alutetium iodide, a bismuth germanate (“BGo”), a lutetium silicate, oranother suitable compound. In a particular embodiment, the inorganicscintillation particles can include NaI(Tl), CaF₂(Eu), PbS, LaBr₃(Ce),BGO, or a lutetium yttrium silicate. Any of the foregoing compounds mayinclude a dopant, wherein the dopant is any of the rare earth elementsor TI. The polymer matrix can include the polymer matrix material asdescribed with respect to the organic scintillation material within thegamma sensitive layers 324.

The scintillation member 320 can be made relatively large because lightis readily transmitted throughout the gamma sensitive layers 324. Ascompared to the gamma sensitive layers 324, visible light is not asreadily transmitted along the length of the neutron sensitive layers322. A synergistic combination of the neutron and gamma sensitive layers322 and 324 can allow scintillating light from neutron radiationgenerated within the neutron sensitive layers 322 to enter the gammasensitive layers 324 and be transmitted to the photosensor 340 via thegamma sensitive layers 324. In an embodiment, the number of the gammasensitive layers 324 is greater than the number of the neutron sensitivelayers 322. In a particular embodiment, scintillation member 320 has onemore of the gamma sensitive layers 324 than the neutron sensitive layers322. In the embodiment as illustrated in FIG. 3, the scintillationmember 320 has five gamma sensitive layers 324 and four neutronsensitive layers 322. More or fewer gamma sensitive layers 324 andneutron sensitive layers 322 can be used. For example, the scintillationmember can include 1, 2, 3, 9, 20, or more of the neutron sensitivelayers 322 or the gamma sensitive layers 324.

On a relative basis, the gamma sensitive layers 324 can be thicker thanthe neutron sensitive layers 322. In an embodiment, the gamma sensitivelayers 324 can be at least approximately 2 times thicker than theneutron sensitive layers 322, and in another embodiment, the gammasensitive layers 324 can be at least approximately 5 times thicker thanthe neutron sensitive layers 322. In a further embodiment, the gammasensitive layers 324 can be at least approximately 25 or even 50 timesthicker than the neutron sensitive layers 322. With respect to actualthicknesses, each of the gamma sensitive layers 324 can be at leastapproximately 1 mm thick, and in another embodiment, each of the gammasensitive layers 324 may be no greater than approximately 60 mm thick.Each of the neutron sensitive layers 322 can be at least approximately0.1 mm thick, and in another embodiment, each of the neutron sensitivelayers 322 may be no greater than approximately 1 mm thick. In aparticular embodiment, the neutron sensitive layers can have a thicknessin a range of approximately 0.2 to 0.5 mm.

An optical coupling material (not illustrated) may be disposed betweeneach immediately adjacent pair of neutron and gamma sensitive layers 322and 324. The optical coupling material can help to improve internalreflection within the gamma sensitive layers 324. In an embodiment, theindex of refraction of the optical coupling material is less than theindex of refraction of the polymer matrix used in the gamma sensitivelayers 324. In another embodiment, the index of refraction of theoptical coupling material is less than approximately 1.49. In aparticular embodiment, the optical coupling material includes a siliconerubber that has an index of refraction of approximately 1.42. In anotherembodiment, the index of refraction of the optical coupling material isless than approximately 1.42. In another particular embodiment, theoptical coupling material includes a fluoropolymer. The optical couplingmaterial may have a thickness no greater than approximately 0.5 mm.

When neutron radiation is received by the apparatus 300, scintillatinglight is generated within a neutron sensitive layer 322 and suchscintillating light passes into a gamma sensitive layer 324. When thegamma sensitive layer 324 includes a wavelength shifting fluorescentmaterial, the scintillating light is absorbed and shifted to anotherwavelength due to the fluorescent material within the gamma sensitivelayer 324 and is transmitted as fluorescent light through the gammasensitive layer 324 to the photosensor 340. When gamma radiation isreceived by the apparatus 300, scintillating light is generated within agamma sensitive layer 324. When the gamma sensitive layer 324 includesthe wavelength shifting fluorescent material, the scintillating light isshifted to another wavelength in response to the fluorescent materialwithin the gamma sensitive layer 324 and is transmitted as fluorescentlight through the gamma sensitive layer 324 to the photosensor 340.

The photosensor 340 receives the light (scintillating light, fluorescentlight, or any combination thereof) and converts the light to anelectronic pulse that is sent to a processing module, such as theprocessing module 120 in FIG. 1. The pulse analyzer within theprocessing module 120 can distinguish electronic pulses corresponding toneutron radiation from electronic pulses corresponding to gammaradiation based at least in part on the decay time of the light reachingthe photosensor 340. In an embodiment, if the decay time is relativelylong, the processing module 120 will send a signal to the radiationcounter 182 that counts neutron radiation, and if the decay time isrelatively short, the processing module 120 will send a signal to theradiation counter 184 that counts gamma radiation events.

In another embodiment as illustrated in FIG. 4, an apparatus 400includes a radiation sensor 410 that is coupled to differentphotosensors 442 and 444. In an embodiment, the photosensor 442 can havea relatively high quantum efficiency with respect to one color of light,for example, orange light, and the photosensor 444 can have a relativelyhigh quantum efficiency with respect to another color of light, forexample, green light. In a particular embodiment, a filter may bedisposed between the scintillating member 420 and either or bothphotosensors 442 and 444. For example, a filter between thescintillation member 420 and the photosensor 442 may filter out greenlight and allow orange light to pass, and a different filter between thescintillation member 420 and the photosensor 444 may filter out orangelight and allow green light to pass. A neutron moderator may surroundthe scintillation member 420 but is not illustrated in FIG. 4.

The neutron sensitive layers 322 may have any composition and thicknessas previously described. The gamma sensitive layers 424 may have anycomposition and thickness as previously described with respect to thegamma sensitive layers 324. As compared to gamma sensitive layers 324,the gamma sensitive layers 424 may have less or different fluorescentmaterials to take advantage of the different photosensors 442 and 444.For example if the scintillating light from the neutron sensitive layers322 is orange, a fluorescent material used to convert such light togreen light would not be needed. Therefore, scintillating light from theneutron sensitive layers 322 can be transmitted along the gammasensitive layer 424 and be received by the photosensor 442. When afilter is used between the scintillation member 420 and the photosensor444, the filter may significantly reduce or substantially prevent orangelight from reaching the photosensor 444. The gamma sensitive layers 424can include a fluorescent material that shifts scintillating light fromgamma radiation to green light that can be transmitted along the gammasensitive layers 424 and be received by the photosensor 444. When afilter is used between the scintillation member 420 and the photosensor442, the filter may significantly reduce or substantially prevent greenlight from reaching the photosensor 442.

When neutron radiation is received by the apparatus 400, scintillatinglight is generated within a neutron sensitive layer 322 and suchscintillating light passes into a gamma sensitive layer 424. When thegamma sensitive layer 424 includes a wavelength shifting fluorescentmaterial, the scintillating light is shifted to another wavelength inresponse to the fluorescent material within the gamma sensitive layer424 and is transmitted as fluorescent light through the gamma sensitivelayer 424 to the photosensor 442. When gamma radiation is received bythe apparatus 400, scintillating light is generated within a gammasensitive layer 424. When the gamma sensitive layer 424 includes thewavelength shifting fluorescent material, the scintillating light isshifted to another wavelength in response to the fluorescent materialwithin the gamma sensitive layer 424 and is transmitted as fluorescentlight through the gamma sensitive layer 424 to the photosensor 444.

When neutron radiation is sensed by a neutron sensitive layer 322 in thescintillation member 420, the photosensor 442 receives the light andconverts the light to an electronic pulse that is sent to a processingmodule, such as the processing module 220 in FIG. 2. Because theprocessing module 220 receives a signal from the photosensor 442, theprocessing module 220 can determine that neutron radiation is receivedby the apparatus 400 and send a signal to the radiation counter 282 thatcounts neutron radiation. When gamma radiation is sensed by a gammasensitive layer 424 in the scintillation member 420, the photosensor 444receives the light and converts the light to an electronic pulse that issent to a processing module, such as the processing module 220 in FIG.2. Because the processing module 220 receives a signal from thephotosensor 444, the processing module 220 can determine that gammaradiation is received by the apparatus 400 and send a signal to theradiation counter 284 that counts gamma radiation.

Embodiments described herein can be used to make radiation sensors thatcan detect more than one targeted radiation and can be scaled to largedimensions. In a particular embodiment, the gamma sensitive layers canbe relatively transparent to visible light, and therefore, the size ofthe gamma sensitive layers may be limited by issues not related to thetransmission of light. For example, the size of the gamma sensitivelayers may be limited by how large a polymer sheet or scintillationfibers may be cast or otherwise formed. The neutron sensitive layers maynot have sufficient transmission over longer distances. By allowinglight to enter a gamma sensitive layer from a neutron sensitive layer,such light that originated from the neutron sensitive layer can be morereadily transmitted to a photosensor that is located adjacent to an endof the gamma sensitive layer. If the neutron sensitive layer cannot bemanufactured as a single sheet as large as a sheet having the gammasensitive layer, then different neutron sensitive layers can be tiled tomatch more closely the size of sheet having the gamma sensitive layer.Thus, a radiation sensor can be fabricated having a dimension of atleast approximately 1.8 m (approximately 70 inches). The dimension cancorrespond to a height or a diagonal dimension of the active area of theradiation sensing portion of the radiation detection system.

A radiation detection system may be configured in different arrangementsas needed or desired. For example, if the cost of or space taken up byphotosensors is an issue, a single photosensor can be used inconjunction with a pulse analyzer to determine which type of radiationhas been detected. One or more fluorescent materials may be includedwithin the gamma sensitive layers so that the wavelengths of fluorescentlight may be closer to the maximum quantum efficiency of thephotosensor. Because the scintillating light, and fluorescent light ifpresent, has different decay times as between neutron radiation andgamma radiation, the pulse analyzer, such as within a processing module,can monitor decay times of the light received by the photosensor todetermine if gamma radiation or neutron radiation is detected.

Instead of a pulse analyzer, different photosensors responding todifferent wavelengths of light may be used. Thus, less complicatedhardware or software may used downstream of the photosensors, such as aprocessing module. Referring to FIG. 4, an electronic pulsecorresponding to detected neutron radiation will be output from thephotosensor 442, and an electronic pulse corresponding to detected gammaradiation will be output from the photosensor 444.

In alternative embodiments, the radiation detection system may beconfigured to detect different targeted radiation, such as x-rays, betaparticles, etc. If the two different targeted radiations produce similarelectronic pulses from a single photosensor, the radiation detectionsystem as illustrated in FIG. 4 may be useful. In a particular example,the different targeted radiation may produce scintillating light orfluorescent light having emission maxima at different wavelengths. Theuse of different photosensors and potentially optical filters can allowidentification of a particular targeted radiation to be made morereadily, and potentially more quickly.

EXAMPLE

The concepts described herein will be further described in the followingexample, which does not limit the scope of the invention described inthe claims.

The example is provided to demonstrate that a radiation detection systemcan be used to detect gamma radiation and neutron radiation and usepulse shape analysis to distinguish between gamma radiation and neutronradiation. Referring to FIG. 5, the radiation sensor includes anassembly 50 that has four layers 54 of BC-704™ brand material, which isa neutron sensitive layer that includes ⁶Li and ZnS(Ag). Each layer 54has a thickness in a range of 0.2 to 0.5 mm (0.01 to 0.02 inches). Theassembly 50 further has five layers 52 of a gamma radiation sensitivelayer that includes p-terphenyl, bis-MSB, and abenzoxanthene-dicarboxylic acid imide within a PVT matrix. Each layer 52has a nominal thickness of 10 mm (0.4 inches). Each layer 54 is disposedbetween two immediately adjacent layers of layers 52, and thus, theradiation sensor has alternating layers of BC-704™ brand material andp-terphenyl, bis-MSB, and a benzoxanthene-dicarboxylic acid imide withina PVT matrix. The assembly 50 has a length (dimension 56 in FIG. 5) of64 cm (25 inches) and a width (dimension 58 in FIG. 5) of 13 cm (5inches). The assembly 50 is wrapped in a layer of TEFLON-brand material,which in turn is wrapped in a layer of black paper. A photodetector (notillustrated in FIG. 5) includes an ADIT™-brand photomultiplier tube(ADIT of Sweetwater, Tex., USA) having 13 cm (5 inch) nominal diameterand is grease coupled to an end of the radiation sensor. Signals fromthe photodetector are provided to an ORTEC®-brand Pulse Shape SensitiveDetector (Advanced Measurement Technology of Oak Ridge, Tenn., USA, notillustrated in FIG. 5) to produce spectra.

A background spectrum (no significant gamma radiation source or neutronsource near the radiation sensor) is noted as “Background” in FIG. 6.The counts to the left of channel 175 are background gamma radiation.The counting rate in this region is 276.4 counts per second (cps). Alsoevident between channels 175 and 400 is a small amount of backgroundneutron radiation, approximately 0.96 cps.

A 9.67 microcurie Cs-137 (gamma radiation) source is placedapproximately 15 cm from the mid point of the radiation sensor. Thespectrum obtained is noted as “Gamma” in FIG. 6. The count rate in thewindow below channel 175 increases to 3851 cps while the count rate inthe window between channels 175 and 400 remains essentially constant at1.06 cps. The bulging on the right side of the peak is unusual and maybe due to pulse pile-up. The bulge disappears when the source is movedback to 50 cm from the radiation sensor.

The Cs-137 (gamma radiation) source is removed, and an AmBe (mainlyneutron) source in its moderator is positioned at approximately 200 cmfrom the radiation sensor. The spectrum obtained is noted as “Neutrons”in FIG. 6.

As can be clearly seen in FIG. 6, gamma radiation and neutron radiationcan be readily distinguished from each other by pulse shape analysis ofthe spectra. The valley between the gamma and neutron peaks occurs atchannel 110, but to avoid gamma spillover into the neutron window, thethreshold is kept at channel 175. For this example, the count rates were690.2 cps for the gamma window and 132.9 cps for the neutron window.Thus, the radiation detection system is sensitive to both gammaradiation and neutron radiation and provides the capability ofdistinguishing between gamma radiation and neutron radiation by usingindependent counting channels based on pulse shape. Skilled artisansknow that differences in pulse shape can be determined by the decay timeof the scintillation pulse and properties of the measurementelectronics.

Many different aspects and embodiments are possible. Some of thoseaspects and embodiments are described below. After reading thisspecification, skilled artisans will appreciate that those aspects andembodiments are only illustrative and do not limit the scope of thepresent invention. Additionally, those skilled in the art willunderstand that some embodiments that include analog circuits can besimilarly implemented using digital circuits, and vice versa.

In a first aspect, a radiation sensor can include a first layerincluding a first scintillation material to produce first light inresponse to receiving a first targeted radiation. The radiation sensorcan also include a second layer including a second scintillationmaterial to produce second light in response to receiving a secondtargeted radiation, wherein the first scintillation material isdifferent from the second scintillation material, and the first targetedradiation is different from the second targeted radiation. The firstlayer can be configured to receive the second light

In an embodiment of the first aspect, the first layer is furtherconfigured to produce third light from the second light within the firstlayer. In a particular embodiment, the first layer is configured toproduce fourth light from the first light. In a more particularembodiment, the first layer is configured to produce fifth light fromthe fourth light, wherein the third light and fifth light have emissionmaxima at substantially a same wavelength. In a further embodiment, thesame wavelength is in a range of approximately 500 nm to approximately600 nm. In another even more particular embodiment, the third light hasan emission maximum at a third wavelength, the fourth light has anemission maximum at a fourth wavelength, and the third and fourthwavelengths are within approximately 100 nm of each other.

In a particular embodiment of the first aspect, the first layer furtherincludes a first fluorescent material capable of producing the thirdlight from the second light, and a second fluorescent material capableof producing the fourth light from the first light. In a more particularembodiment, the first fluorescent material includes p-terphenyl,bis-MSB, and a benzoxanthene-dicarboxylic acid imide and the secondfluorescent material includes ZnS.

In still a further embodiment of the first aspect, the radiation sensorfurther includes another first layer, wherein the second layer isdisposed between the first layers. In another embodiment, the radiationsensor further includes other first layers and at least one additionalsecond layer, wherein the radiation sensor includes a laminate compositeof alternating first and second layers. In still another embodiment, thefirst layer is in a form of fibers. In a particular embodiment, thefirst layer further includes a polymer matrix, wherein the firstscintillation material is within the polymer matrix. In a furtherembodiment, the radiation sensor further includes an optical couplingmaterial between the first and second layers, wherein an index ofrefraction of the optical coupling material is less than an index ofrefraction of the first layer. In a particular embodiment, the index ofrefraction of the optical coupling material is no greater thanapproximately 1.49. In a more particular embodiment, the first layerfurther includes a polyvinyl toluene, a polystyrene, apolymethylmethacrylate, or any combination thereof, and the opticalcoupling material includes a silicon rubber or a fluoropolymer.

In another embodiment of the first aspect, the first layer is thickerthan the second layer. In a particular embodiment, the first layer is atleast approximately 2 times thicker than the second layer. In anotherparticular embodiment, the first layer is at least approximately 5 timesthicker than the second layer. In still another particular embodiment,the first layer is at least approximately 25 or even 50 times thickerthan the second layer. In yet another embodiment, the first layer ismore sensitive to gamma radiation than to neutron radiation, and thesecond layer is more sensitive to neutron radiation than to gammaradiation.

In a further embodiment of the first aspect, the second scintillationmaterial includes a first compound to produce a secondary particle inresponse to receiving the neutron, and a second compound to produce thesecond light in response to receiving the secondary particle. In aparticular embodiment, the first compound includes ⁶Li or ¹⁰B. In a moreparticular embodiment, the second compound includes ZITS, CaWO₄, Y₂SiO₅,ZnO, CaF₂, or ZnCdS. In still another particular embodiment, the firstscintillation material includes an organic material. In a moreparticular embodiment, the organic material includes1,4-bis(5-phenyloxazol-2-yl)benzene, 2,5-diphenyloxazole, p-terphenyl,naphthalene, 1,4-bis[2-methylstyryl benzene], or 1,1,4,4-tetraphenyl-1,3butadiene. In yet another particular embodiment, the first scintillationmaterial includes an inorganic material. In a more particularembodiment, the inorganic material includes a sodium iodide, a calciumfluoride, a cesium iodide, a cesium lithium elpasolite, a lanthanumbromide, a lanthanum chloride, a lutetium iodide, a bismuth germanate,or a lutetium silicate.

In a second aspect, a radiation detection system can include a radiationsensor and a first photosensor. The radiation sensor can include a firstlayer including a first scintillation material to produce first light inresponse to receiving a first targeted radiation. The radiation sensorcan further include a second layer including a second scintillationmaterial to produce second light in response to receiving a secondtargeted radiation, wherein the first scintillation material isdifferent from the second scintillation material, and the first targetedradiation is different from the second targeted radiation. The firstlayer can be configured to receive and transmit the second light. Thefirst photosensor can be coupled to the first layer.

In an embodiment of the second aspect, the first layer is configured toreceive the second light. In a particular embodiment, the first layer isfurther configured to produce third light from the second light withinthe first layer. In a more particular embodiment, the first layer isconfigured to produce fourth light from the first light. In an even moreparticular embodiment, the first layer is configured to produce fifthlight from the fourth light, wherein the third light and fifth lighthave emission maxima at substantially a same wavelength. In a furtherembodiment, the same wavelength is in a range of approximately 500 nm to600 nm. In another even more particular embodiment, the third light hasan emission maximum at a third wavelength, the fourth light has anemission maximum at a fourth wavelength, and the third and fourthwavelengths are within approximately 100 nm of each other.

In yet another embodiment of the second aspect, the first layer furtherincludes a first fluorescent material capable of producing the thirdlight from the second light, and a second fluorescent material capableof producing the fourth light from the first light. In a particularembodiment, the first fluorescent material includes p-terphenyl,bis-MSB, and a benzoxanthene-dicarboxylic acid imide, and the secondfluorescent material includes ZnS.

In a further embodiment of the second aspect, the first layer is moresensitive to gamma radiation than to neutron radiation, and the secondlayer is more sensitive to neutron radiation than to gamma radiation. Instill a further embodiment, the radiation detection system furtherincludes a second photosensor coupled to the first layer, wherein thesecond photosensor is different from the first photosensor. In aparticular embodiment, the first photosensor is coupled to a first endof the first layer, and the second photosensor is coupled to the firstlayer at a second end opposite the first end. In yet another embodiment,the first photosensor is an only photosensor coupled to the first layer.In a particular embodiment, the radiation detection system furtherincludes a pulse analyzer coupled to the first photosensor. In anotherparticular embodiment, the radiation detection system further includes areflector, wherein the first photosensor is coupled to a first end ofthe first layer, and the reflector is coupled to the first layer at asecond end opposite the first end.

In another embodiment of the second aspect, the radiation detectionsystem further includes a neutron moderator to convert a fast neutron toa thermal neutron. In still another embodiment, the radiation sensorincludes additional first and second layers, wherein the radiationsensor is configured to include a laminate, wherein the first and secondlayers alternate with each other. In a particular embodiment, each ofthe first layers is at least approximately 2 mm thick. In anotherparticular embodiment, each of the first layers is no greater thanapproximately 60 mm thick. In still another particular embodiment, eachof the second layers is at least approximately 0.1 mm thick. In yetanother particular embodiment, each of the second layers is no greaterthan approximately 1.0 mm thick. In a further particular embodiment,each of the first layers has a thickness in a range of approximately 5mm to approximately 15 mm, and each of the second layers has a thicknessin a range of approximately 0.1 mm to approximately 1.0 mm. In still afurther particular embodiment, the radiation sensor has n+1 first layersand n second layers, wherein n is at least 1. In a more particularembodiment, the radiation sensor has 5 first layers and 4 second layersand having an alternating first layer-second layer configuration. Inanother embodiment, the radiation sensor comprises a plurality ofdiscrete units, wherein each discrete unit includes a second layerbetween two first layers. In yet a further particular embodiment, theradiation detection system further includes an optical couplingmaterial, wherein the optical coupling material is disposed between eachpair of immediately adjacent first and second layers.

In a third aspect, a method of detecting radiation can include providinga radiation sensor of a radiation detection system in an environment,wherein the radiation sensor includes a first radiation sensitive layerand a second radiation sensitive layer, and the first radiationsensitive layer is adapted to transmit scintillation light received fromthe second radiation sensitive layer. The method can further includedetermining whether the environment contained a significant amount ofthe first radiation, the second radiation, or both the first and secondradiation.

In an embodiment of the third aspect, the method further includesgenerating a spectrum based on data collected when the radiation sensoris in the environment. In a particular embodiment, determining whetherthe environment contained a significant amount of the first radiation,the second radiation, or both the first and second radiation comprisesperforming pulse shape analysis on the spectrum. In another embodiment,the radiation sensor has n+1 first radiation sensitive layers and nsecond radiation sensitive layers, wherein n is at least 1, in analternating first radiation sensitive layer-second radiation sensitivelayer configuration. In still another embodiment, the radiation sensorcomprises a plurality of discrete units, wherein each discrete unitincludes a second radiation sensitive layer disposed between two firstradiation sensitive layers. In yet another embodiment, the firstradiation includes gamma radiation, and the second radiation includesneutron radiation.

In a further embodiment of the third aspect, the first radiationsensitive layer has a first pulse time when exposed to first radiation,the second radiation sensitive layer has a second pulse time whenexposed to second radiation, and the second pulse time is at least twotimes longer than the first pulse time. In a particular embodiment, thesecond pulse time is at least three, five, or ten times longer than thefirst pulse time.

Note that not all of the activities described above in the generaldescription or the examples are required, that a portion of a specificactivity may not be required, and that one or more further activitiesmay be performed in addition to those described. Still further, theorder in which activities are listed is not necessarily the order inwhich they are performed.

In a particular embodiment, a method may be described in a series ofsequential actions. The sequence of the actions and the party performingthe actions may be changed without necessarily departing from the scopeof the teachings unless explicitly stated to the contrary. Actions maybe added, deleted, or altered. Also, a particular action may beiterated. Further, actions within a method that are disclosed as beingperformed in parallel may in particular cases be performed serially, andother actions within a method that are disclosed as being performedserially may in particular cases be performed in parallel.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature of any or all the claims.

The specification and illustrations of the embodiments described hereinare intended to provide a general understanding of the structure of thevarious embodiments. The specification and illustrations are notintended to serve as an exhaustive and comprehensive description of allof the elements and features of apparatus and systems that use thestructures or methods described herein. Separate embodiments may also beprovided in combination in a single embodiment, and conversely, variousfeatures that are, for brevity, described in the context of a singleembodiment, may also be provided separately or in any subcombination.Further, reference to values stated in ranges includes each and everyvalue within that range. Many other embodiments may be apparent toskilled artisans only after reading this specification. Otherembodiments may be used and derived from the disclosure, such that astructural substitution, logical substitution, or another change may bemade without departing from the scope of the disclosure. Accordingly,the disclosure is to be regarded as illustrative rather thanrestrictive.

1. A radiation sensor comprising: a first layer including a firstscintillation material to produce first light in response to receiving afirst targeted radiation; and a second layer including a secondscintillation material to produce second light in response to receivinga second targeted radiation, wherein the first scintillation material isdifferent from the second scintillation material, and the first targetedradiation is different from the second targeted radiation, wherein thefirst layer is configured to receive and transmit the second light.2-16. (canceled)
 17. The radiation sensor of claim 1, wherein the firstlayer is thicker than the second layer. 18-21. (canceled)
 22. Theradiation sensor of claim 1, wherein: the first layer is more sensitiveto gamma radiation than to neutron radiation; and the second layer ismore sensitive to neutron radiation than to gamma radiation.
 23. Theradiation sensor of claim 1, wherein the second scintillation materialcomprises: a first compound to produce a secondary particle in responseto receiving the neutron; and a second compound to produce the secondlight in response to receiving the secondary particle.
 24. The radiationsensor of claim 23, wherein the first compound comprises ⁶Li or ¹⁰B. 25.The radiation sensor of claim 23, wherein the second compound includesZnS, CaWO₄, Y₂SiO₅, ZnO, CaF₂, or ZnCdS
 26. The radiation sensor ofclaim 23, wherein the first scintillation material comprises an organicmaterial.
 27. The radiation sensor of claim 26, wherein the organicmaterial comprises 1,4-bis(5-phenyloxazol-2-yl)benzene,2,5-diphenyloxazole, p-terphenyl, naphthalene, 1,4-bis[2-methylstyrylbenzene], or 1,1,4,4-tetraphenyl-1,3 butadiene.
 28. The radiation sensorof claim 23, wherein the first scintillation material comprises aninorganic material.
 29. The radiation sensor of claim 28, wherein theinorganic material comprises a sodium iodide, a calcium fluoride, acesium iodide, a cesium lithium elpasolite, a lanthanum bromide, alanthanum chloride, a lutetium iodide, a bismuth germanate, or alutetium silicate.
 30. A radiation detection system comprising: aradiation sensor comprising: a first layer including a firstscintillation material to produce first light in response to receiving afirst targeted radiation; and a second layer including a secondscintillation material to produce second light in response to receivinga second targeted radiation, wherein the first scintillation material isdifferent from the second scintillation material, and the first targetedradiation is different from the second targeted radiation, wherein thefirst layer is configured to receive and transmit the second light; anda first photosensor coupled to the first layer. 31-33. (canceled) 34.The radiation detection system of claim 32, wherein the first layer isconfigured to produce fifth light from the fourth light, wherein thethird light and fifth light have emission maxima at substantially a samewavelength.
 35. The radiation detection system of claim 34, wherein thesame wavelength is in a range of approximately 500 nm to approximately600 nm.
 36. The radiation detection system of claim 34, wherein thefirst layer further comprises: a first fluorescent material capable ofproducing the third light from the second light; and a secondfluorescent material capable of producing the fourth light from thefirst light.
 37. The radiation detection system of claim 36, wherein thefirst fluorescent material includes p-terphenyl, bis-MSB, and abenzoxanthene-dicarboxylic acid imide.
 38. The radiation detectionsystem of claim 36, wherein the second fluorescent material includesZnS.
 39. The radiation detection system of claim 30, wherein: the firstlayer is more sensitive to gamma radiation than to neutron radiation;and the second layer is more sensitive to neutron radiation than togamma radiation.
 40. The radiation detection system of claim 30, furthercomprising a second photosensor coupled to the first layer, wherein thesecond photosensor is different from the first photosensor. 41-55.(canceled)
 56. A method of detecting radiation comprising: providing aradiation sensor of a radiation detection system in an environment,wherein the radiation sensor includes a first radiation sensitive layerand a second radiation sensitive layer, and the first radiationsensitive layer is adapted to transmit scintillation light received fromthe second radiation sensitive layer; determining whether theenvironment contained a significant amount of the first radiation, thesecond radiation, or both the first and second radiation.
 57. The methodof claim 56, further comprising generating a spectrum based on datacollected when the radiation sensor is in the environment, whereindetermining whether the environment contained a significant amount ofthe first radiation, the second radiation, or both the first and secondradiation comprises performing pulse shape analysis on the spectrum.58-64. (canceled)